This paper presents the results of experiments that determine the chromosomal location of the mouse gene encoding CCAAT/enhancer binding protein (C/EBP) and measure its expression as a function of tissue type and temporal period of development in mice and rats Three alleles of the C/EBP gene were identified according to restriction fragment length polymorphisms The strain distribution pattern of the three alleles was determined in recombinant inbred mouse strains and compared to that of other mouse genes These results mapped the gene to a position within 25 centimorgans (cM) of the structural gene encoding glucose phosphate isomerase on chromosome 7 of the mouse The expression pattern of the C/EBP gene was studied by a combination of nucleic acid hybridization and antibody staining assays High levels of C/EBP mRNA were observed in tissues known to metabolize lipid and cholesterol-related compounds at uncommonly high rates These included liver, fat, intestine, lung, adrenal gland, and placenta More detailed analysis of two of these tissues, liver and fat, showed that C/EBP expression was limited to fully differentiated cells Moreover, analysis of the temporal pattern of expression of C/EBP mRNA in two tissues, liver and intestine, revealed a coordinated induction just prior to birth These observations raise the possibility that the synthesis of C/EBP may be responsive to humoral factors and that modulation in C/EBP expression might mediate coordinated changes in gene expression that facilitate adaptive challenges met during development or during the fluctuating physiological states of adult life

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Tissue-specific expression, developmental regulation, and genetic mapping of the gene encoding CCAAT/enhancer binding protein.

Technological advances have made possible the development of high-resolution genetic linkage maps for the mouse. These maps in turn offer exciting prospects for understanding mammalian genome evolution through comparative mapping, for developing mouse models of human disease, and for identifying the function of all genes in the organism.

A genetic linkage map of the mouse: current applications and future prospects

MANY metabolic diseases affecting the central nervous system are refractory to treatment because the blood–brain barrier restricts entry of therapeutic molecules. It may be possible to deliver therapeutic gene products directly to the brain by transplantation of neural progenitor cells, which can integrate into the murine central nervous system in a cytoarchitecturally appropriate manner1–7. We tested this approach in mucopolysaccharidosis VII (Sly disease), a lysosomal storage disorder of humans, dogs and mice caused by an inherited deficiency of β-glucuronidase8–10 . Lysosomal accumulation of glycosaminoglycans occurs in the brain and other tissues, causing a fatal progressive degenerative disorder, including mental retardation11. Treatments are designed to provide a source of normal enzyme for uptake by diseased cells12–20. We report here that by transplanting β-glucuronidase-expressing neural progenitors into the cerebral ventricles of newborn mice, donor cells engrafted throughout the neuraxis. At maturity, donor-derived cells were present as normal constituents of diverse brain regions. β-Glucu-ronidase activity was expressed along the entire neuraxis, resulting in widespread correction of lysosomal storage in neurons and glia in affected mice.

Neural progenitor cell engraftment corrects lysosomal storage throughout the MPS VII mouse brain.

Transduction characteristics of adeno-associated virus vectors expressing cap serotypes 7, 8, 9, and Rh10 in the mouse brain.

The ability to detect and degrade transcripts that lack full coding potential is ubiquitous but non-essential in lower eukaryotes, leaving in question the evolutionary basis for complete maintenance of this function. One hypothesis holds that nonsense-mediated RNA decay (NMD) protects the organism by preventing the translation of truncated peptides with dominant negative or deleterious gain-of-function potential. All organisms studied to date that are competent for NMD express a structural homolog of Saccharomyces cerevisiae Upf1 p. We have now explored the consequences of loss of NMD function in vertebrates through targeted disruption of the Rent1 gene in murine embryonic stem cells which encodes a mammalian ortholog of Upf1p. Mice heterozygous for the targeted allele showed no apparent phenotypic abnormalities but homozygosity was never observed, demonstrating that Rent1 is essential for embryonic viability. Homozygous targeted embryos show complete loss of NMD and are viable in the pre-implantation period, but resorb shortly after implantation. Furthermore, Rent1 -/- blastocysts isolated at 3.5 days post-coitum undergo apoptosis in culture following a brief phase of cellular expansion. These data suggest that NMD is essential for mammalian cellular viability and support a critical role for the pathway in the regulated expression of selected physiologic transcripts.

Rent1, a trans-effector of nonsense-mediated mRNA decay, is essential for mammalian embryonic viability.

We have characterized a new mutant mouse that has virtually no beta-glucuronidase activity. This biochemical defect causes a murine lysosomal storage disease that has many interesting similarities to human mucopolysaccharidosis type VII (MPS VII; Sly syndrome; beta-glucuronidase deficiency). Genetic analysis showed that the mutation is inherited as an autosomal recessive that maps to the beta-glucuronidase gene complex, [Gus], on the distal end of chromosome 5. Although there is a greater than 200-fold reduction in the beta-glucuronidase mRNA concentration in mutant tissues, Southern blot analysis failed to detect any abnormalities in the structural gene, Gus-sb, or in 17 kb of 5' flanking and 4 kb of 3' flanking sequences. Surprisingly, a sensitive S1 nuclease assay indicated that the relative level of kidney gusmps mRNA responded normally to androgen induction by increasing approximately 11-fold. Analysis of this mutant mouse may offer valuable information on the pathogenesis of human MPS VII and provide a useful system in which to study bone marrow transplantation and gene transfer methods of therapy.

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L M Maltais

Papers

Murine mucopolysaccharidosis type VII. Characterization of a mouse with beta-glucuronidase deficiency.